Improvements relating to apparatus negative pressure wound therapy

ABSTRACT

An apparatus (1) for negative pressure wound therapy comprises a source of reduced pressure (10) and first (22a) and second (26a) chambers, the first chamber being in fluid communication with the source of reduced pressure such that a negative pressure may be generated in the first chamber, the negative pressure being prevented from exceeding a predetermined value by way of a pressure release means (30), and the second chamber comprising means (28) for establishing a fluid connection with a wound. A valve (24) between the first and second chambers permits the negative pressure in the second chamber to increase in response to an increase in the negative pressure in the first chamber and prevents the negative pressure in the second chamber from dropping in response to a drop in the negative pressure in the first chamber.

FIELD OF THE INVENTION

This invention relates generally to negative pressure wound therapy(NPWT), and more specifically to an improved apparatus for performingNPWT.

BACKGROUND TO THE INVENTION

Negative pressure wound therapy (NPWT) involves the application of apressure that is reduced relative to the surroundings (commonly referredto as “negative pressure”) to a wound, which causes mechanicalcontraction of the wound and removal of wound fluid from the wound, thuspromoting formation of granulation tissue and accelerating woundhealing. The technique is particularly effective in the treatment ofslow healing wounds such as chronic leg ulcers and large open wounds. Anocclusive dressing is applied to the wound and forms a seal around thewound under which a negative pressure can be established. The occlusivedressing is traversed by a drainage tube, which is connected to a sourceof negative pressure which enables a source of reduced pressure to beapplied to a wound and for wound fluid to be drained from the wound. Thenegative pressure that is applied to a wound is typically around 100mmHg, although a negative pressure in the range of 80-120 mmHg isusually tolerated as movement of the patient or direct pressure on thewound can cause the pressure at the wound site to fluctuate. However, itis generally accepted that the application of a negative pressure inexcess of 120 mmHg to a wound is undesirable.

Apparatus for NPWT typically includes means for carefully managing thenegative pressure that is applied to the wound in order to ensure thatit is retained in the desired range of 80-120 mmHg. In particular, theapparatus must prevent the negative pressure that is applied to thewound from dropping below 80 mmHg as a result of leaks in NPWTapparatus, which may occur at the wound site as a result of theocclusive dressing not forming a complete seal around the wound, or viathe source of reduced pressure as conventional sources of reducedpressure such as vacuum pumps do not typically have an air tightconstruction. In addition, the apparatus must also prevent the negativepressure that is applied to the wound from exceeding 120 mmHg as aresult of excessive activation of the source of reduced pressure.

Accordingly, apparatus for NPWT includes a complex arrangement ofconduits and valves for the management of the negative pressure that isapplied to the wound. These arrangements include numerous joints betweencomponents, all of which are potential sources of leaks and requireprecision assembly in order to reduce the incidence of leaks, which addssignificantly to the cost of manufacturing NPWT apparatus. In addition,many NPWT systems include complex valves such as electronic valves thatare expensive and prone to failure.

There is therefore a need for an apparatus for NPWT that comprises arobust and simple means of controlling the negative pressure that isapplied to a wound, does not require a complex arrangement of conduitsand valves and does not require precision assembly.

There has now been devised an apparatus for negative pressure woundtherapy that overcomes or substantially mitigates the above mentionedand/or other problems associated with the prior art.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided anapparatus for negative pressure wound therapy comprising:

-   -   a source of reduced pressure;    -   a first chamber in fluid communication with the source of        reduced pressure such that the source of reduced pressure is        operable to generate a negative pressure in the first chamber;    -   a pressure release means that prevents the negative pressure in        the first chamber from exceeding a predetermined negative        pressure value;    -   a second chamber comprising means for establishing fluid        communication between the second chamber and a wound;    -   a valve located between the first chamber and the second        chamber, the valve permitting the negative pressure in the        second chamber to increase in response to an increase in the        negative pressure in the first chamber, and preventing the        negative pressure in the second chamber from dropping in        response to a drop in the negative pressure in the first        chamber.

The apparatus may be operated by establishing fluid communicationbetween the second chamber and the wound by a suitable means andactivating the source of reduced pressure. The operation of the sourceof reduced pressure generates a negative pressure in the first chamber,which in turn generates a negative pressure in the second chamber andthe application of a negative pressure to the wound that is in fluidcommunication with the second chamber. The pressure release meansprevents the negative pressure in the first chamber, and hence thenegative pressure in the second chamber and that is applied to thewound, from exceeding a predetermined negative pressure value,regardless of the negative pressure that is generated by the source ofreduced pressure. Accordingly, the predetermined negative pressure valueis the maximum negative pressure that the apparatus is capable ofapplying to a wound. The predetermined negative pressure value ispreferably 120 mmHg or higher and for example may be 125 mmHg, 130 mmHg,140 mmHg or 150 mmHg.

The source of reduced pressure may be deactivated in response to thenegative pressure that is applied to the wound has reached a desiredlevel. The negative pressure in the first chamber may then drop, forexample due to the entry of gas into the first chamber via the source ofreduced pressure or the pressure release means. The valve locatedbetween the first chamber and the second chamber prevents the negativepressure in the second chamber, and consequently the negative pressurethat is applied to the wound, from dropping in response to a drop in thenegative pressure in the first chamber. The negative pressure that isapplied to the wound may nevertheless drop over time, for example due tothe entry of gas into the second chamber or the wound. The source ofreduced pressure may be activated in response to the negative pressurethat is applied to the wound dropping below a desired level.

The apparatus may further comprise a means for detecting the negativepressure that is applied to the wound. This may comprise means fordetecting the negative pressure in the second chamber, and for examplemay be in fluid communication with the second chamber, as the secondchamber and the wound are in fluid communication and hence are atsubstantially the same negative pressure during operation of theapparatus.

The means for detecting the negative pressure that is applied to thewound may be operably coupled to the source of reduced pressure, forexample such that the source of reduced pressure is deactivated inresponse to the negative pressure that is applied to the wound reachinga desired level and/or the source of reduced pressure is activated inresponse to the negative pressure that is applied to the wound droppingbelow a desired level. This arrangement may enable the apparatus tomaintain the negative pressure that is applied to the wound at a desiredlevel for as long as the apparatus is in operation without the need forfurther intervention by an operator.

The desired level of negative pressure that is applied to the wound maybe between 75 and 125 mmHg, 80 and 120 mmHg, 90 and 110 mmHg, or about100 mmHg. The means for detecting the negative pressure that is appliedto the wound may be operably coupled to the source of reduced pressurevia a programmable computer processor that permits the desired level ofnegative pressure that is applied to the wound to be varied.

The means for detecting the negative pressure that is applied to thewound may be an electronic pressure sensor such as a piezoresistiveelectronic pressure sensor. One pressure sensor that is suitable for usewith this invention is the 2SMPP-03 MEMS Gauge Pressure Sensor by OmronCorporation.

The source of reduced pressure may be a vacuum pump such as a diaphragmvacuum pump, an electromagnetic vacuum pump or a piezoelectric vacuumpump. The source of reduced pressure may be compact and in particularmay have a maximum dimension of less than 100 mm, less than 80 mm, lessthan 60 mm or less than 40 mm, and may occupy a volume of less than 10cm³, less than 8 cm⁴, less than 6 cm³ or less than 4 cm³. The source ofreduced pressure is typically the most bulky component of apparatus fornegative pressure wound therapy and hence the use of a compact source ofreduced pressure is desirable to permit the apparatus to improve thehandling and mobility of the apparatus. One example of a vacuum pumpthat is suitable for use with this invention is the KPV08A-3A MicroVacuum Pump by Koge Micro Tech Co Ltd.

The source of reduced pressure may be powered by electricity.Accordingly, the apparatus may further comprise a power source for thesource of reduced pressure. The power source may comprise one or morebatteries, or means for the connection of one or more batteries to theapparatus. In one preferred embodiment, the one or more batteries may bestandard batteries such as AA or AAA batteries. The source of reducedpressure preferably has a relatively low power consumption in order toenable it to run for extended periods without the need to replacebatteries. In particular, the maximum power consumption of the source ofreduced pressure may be less than 5 W, less than 3 W or less than 2 W.

The first and second chambers may be defined by suitable housings. Thehousings may be in the form of a tube or the like, including a branchedtube such as a manifold or T-piece, in which case the first and secondchambers correspond to the internal volume of the tube or the like. Thehousings that define the first and second chambers may be structurallydifferent, but are preferably structurally the same in order to simplifyassembly of the apparatus and reduce manufacturing cost.

The housings preferably include openings through which the first andsecond chambers can form a connection with the other components of theapparatus, including the source of reduced pressure, the valve locatedbetween the first chamber and the second chamber, the pressure releasemeans and the means for detecting the negative pressure that is appliedto the wound. The connections between the housings and the othercomponents of the apparatus are preferably air-tight or substantiallyair-tight. The housings may engage with the other components of theapparatus via an interference fit or barbed connections in order tosimplify assembly of the apparatus and reduce manufacturing cost.

The housings may comprise a relatively soft material in the regions inwhich they engage the other components of the apparatus in order tofacilitate the assembly of the components of the apparatus and providegood surface area contact and hence the formation of an effective sealbetween the components of the apparatus without the need for precisionassembly. In one preferred embodiment, the housings are formed entirelyof the relatively soft material. Suitable relatively soft materialsinclude thermoplastic elastomers such as thermoplastic polyurethane orstyrene-butadiene rubber.

The housings are preferably formed of a single component in order toeliminate the need for joints between multiple components that couldpermit the entry of gas into the chambers during the operation of theapparatus. The housing is preferably formed by a moulding process suchas injection moulding. In particular, 3D printing has been found to begenerally unsuitable for the formation of the housing in cases wherethis produces a porous structure that is not sufficiently air-tight foruse with this invention.

The volume of the first and second chambers is preferably no greaterthan is necessary for the operation of the apparatus in order to reducethe volume of gas that must be extracted from the chambers in order togenerate the desired negative pressure. In particular, the volume of thefirst chamber and the second chamber may be less than 5 cm³, less than 3cm³, or less than 1 cm³, The first and second chambers may have the sameor different volumes.

The valve located between the first chamber and the second chamber mayoperate by substantially preventing gas flow from the first chamber intothe second chamber and permitting gas flow from the second chamber intothe first chamber. The valve preferably operates passively in responseto changes in the negative pressure in the first chamber and the secondchamber. In particular, the valve may substantially prevent gas flowfrom the first chamber into the second chamber when the negativepressure in the second chamber exceeds the negative pressure in thefirst chamber, and may permit gas flow from the second chamber into thefirst chamber when the negative pressure in the first chamber exceedsthe negative pressure in the second chamber. The valve may permit gasflow from the second chamber into the first chamber when the negativepressure in the first chamber exceeds the negative pressure in thesecond chamber by less than 10 mmHg, less than 8 mmHg or less than 5mmHg.

The valve located between the first chamber and the second chamber ispreferably a one-way valve, and examples of suitable one-way valves arediaphragm valves, ball and spring valves and swing/tilt valves. Onevalve that is suitable for use with this invention is the SCV 67220Barbed Check Valve by Nordson Corporation.

The pressure release means may operate by permitting the entry of gasinto the first chamber. The pressure release means may communicatebetween the first chamber and a source of gas, such as atmospheric gasin the surroundings. The pressure release means may be a valve mayprevent the entry of gas into the first chamber until the predeterminednegative pressure value is reached, at which point the valve may open topermit entry of gas into the first chamber and hence prevent any furtherincrease in negative pressure. A wide range of suitable pressure releasevalves are available including electronically operated valves ormechanical vales, such as ball and spring valves.

However, in one preferred embodiment, the pressure release means remainspermanently open to the entry of gas into the first chamber such thatthe extraction of gas from the first chamber by the source of reducedpressure and the entry of gas into the first chamber via the pressurerelease means reach equilibrium at the predetermined negative pressurevalue. This form of pressure release means does not contain moving partsand hence possesses improved reliability compared with electronicallyoperated or mechanical vales. Suitable valves of this kind include flowrestrictors such as precision orifices. One precision orifice that issuitable for use with this invention is the F2815 Series PrecisionOrifice Of 0.004″.

The means for establishing fluid communication between the secondchamber and a wound may comprise a connector, such as a Luer lock oranother conventional medical connector. The means preferably permits theformation of an air-tight or substantially air-tight connection betweenthe second chamber and a wound. The means may permit connection betweenthe second chamber and a one end of a conduit that communicates with awound dressing for negative pressure wound therapy.

Thus, according to a second aspect of this invention, there is provideda system for negative pressure wound therapy comprising:

-   -   an apparatus for negative pressure wound therapy according to        the first aspect of this invention; and,    -   a wound dressing for negative pressure wound therapy in fluid        communication with the second chamber of the apparatus.

The wound dressing preferably comprises a conduit by which it is incommunication with the second chamber of the apparatus. The conduit maytraverses the backing layer and hence permits a negative pressure to beapplied between the wound dressing and the wound by connecting theconduit to the second chamber. Suitable conduits include conventionalmedical tube including plastics tube formed of, for example, silicone orpolyvinylchloride. The conduit is preferably transparent or at leasttranslucent to enable blockages to be easily identified. In addition,the conduit may have an external diameter of between 4 mm and 10 mm,between 5 mm and 8 mm or about 6 mm.

The wound dressing may be any conventional wound dressing for negativepressure wound therapy and in particular may comprise a backing layerthat is substantially impermeable to gas, and a skin contact layer thatis able to form a seal against the skin in the regions surrounding thewound, such that a negative pressure can be established between thewound dressing and the wound. The backing layer may have a low degree ofpermeability to allow for the transmission of moisture vapour, and inparticular may be formed of a sheet of microporous plastics materialsuch as polyurethane. The skin contact layer preferably carries anon-adherent or low-adherence adhesive, most preferably a soft siliconegel. There are preferably perforations or gaps in the soft silicone gelin order to permit transmission of moisture vapour away from the skinand hence maintain good adhesion and a proper seal around the wound. Thewound dressing may further comprise a wound packing element formed of amass of resilient gas-permeable material such as foam, which ensures theeven distribution of a negative pressure throughout the wound.

In one preferred embodiment, the wound dressing comprises an absorbentmaterial, and preferably a superabsorbent material, that is capable ofabsorbing large quantities of wound exudate and hence may eliminate theneed for a canister or other container for collecting excess woundexudate. “Superabsorbent material” in the context of this inventionmeans a material that is capable of absorbing many times its own mass ofwater (eg up to 200, 300, 400, 500 or more times its own mass of water).Suitable superabsorbent materials include alginate, polyacrylate (iesalts of polyacrylic acid, such as sodium polyacrylate), polyacrylamidecopolymers, ethylene maleic anhydride copolymer, carboxymethylcellulose,polyvinylalcohol copolymers, polyethylene oxide and starch-graftedcopolymers of polyacrylonitrile. The super absorbent material may bepresent in particulate form, in which case the particles may beincorporated into a carrier material.

The apparatus according to the first aspect of this invention may bedisposable. In particular, the apparatus may be programmed to ceasefunctioning after a set period of time, such as 60 days, 45 days or 30days, from the time of the first operation of the apparatus. The wounddressing may also be disposable and in particular may be replaced oncethe absorbent or wound packing materials become saturated with woundexudate. The lifespan of the wound dressing may therefore besignificantly shorter than the lifespan of the apparatus.

Thus, according to a third aspect of this invention, there is provided akit for negative pressure wound therapy comprising:

-   -   an apparatus for negative pressure wound therapy according to        the first aspect of this invention; and,    -   a plurality of wound dressings for negative pressure wound        therapy adapted for the establishment of fluid communication        with the second chamber of the apparatus.

According to a fourth aspect of this invention, there is provided amethod of negative pressure wound therapy comprising:

-   -   applying a wound dressing for negative pressure wound therapy to        a wound;    -   establishing fluid communication between the wound dressing and        the second chamber of the apparatus according to the first        aspect of this invention; and,    -   activating the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail, by way ofillustration only, with reference to the accompany drawings, in which

FIG. 1 is a perspective view of an exemplary embodiment of an apparatusfor negative pressure wound therapy according to this invention.

FIG. 2 is an exploded perspective view of the apparatus for negativepressure wound therapy of FIG. 1.

FIG. 3 is an additional exploded perspective view of the apparatus fornegative pressure wound therapy of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 to 3 depict an exemplary embodiment of an apparatus for negativepressure wound therapy according to this invention, which is generallydesignated 1. The apparatus 1 comprises a source of reduced pressure inthe form of a vacuum pump 10, a connector assembly 20, and a printedcircuit board (PCB) 40. The PCB 40 comprises a pair of projections 42 towhich the vacuum pump 10 is soldered in order to secure the vacuum pump10 to the PCB 40. The connector assembly 20 engages with the vacuum pump10 via a vacuum port 12 located on the vacuum pump 10.

The connector assembly 20 comprises a first tubular connector 22, aone-way valve 24, a second tubular connector 26 and a port 28. The firsttubular connector 22 comprises a housing that defines a first chamber 22a, and which is formed of a primary tube 22 b having an opening at eachend that communicates between the first chamber 22 a and the exterior ofthe connector 22, and a side tube 22 c that branches from the primarytube 22 b and has an opening at its free end that communicates betweenthe first chamber 22 a and the exterior of the connector 22. The secondtubular connector 26 is of identical construction to the first tubularconnector 22 and comprises a housing that defines a second chamber 26 a,and which is formed of a primary tube 26 b and a side tube 26 c.

The first tubular connector 22 engages with the vacuum port 12 via theopening at the end of its primary tube 22 b that is proximal to thevacuum pump 10, and engages with the one-way valve 24 via the opening atthe end of its primary tube 22 b that is distal to the vacuum pump 10.The second tubular connector 26 engages with the one-way valve 24 viathe opening at the end of its primary tube 26 b that is proximal to thevacuum pump 10, and engages with the port 28 via the opening at the endof its primary 26 b tube that is distal to the vacuum pump 10.

The one-way valve 24 is and permits the passage of gas from the secondchamber 26 a into the first chamber 22 a, but prevents the passage ofgas from the first chamber 22 a into the second chamber 26 a, The port28 is a conventional Luer lock that is capable of forming asubstantially air-tight connection with a medical tube for establishingfluid communication with a wound site.

The first tubular connector 22 further comprises a pressure releasevalve 30 in the form of a precision orifice that is located in theopening in the free end of its side tube 22 c. The pressure releasevalve 30 permits the entry of gas into the first chamber 22 a from thesurroundings in order to prevent the level by which the pressure in thefirst chamber 22 a is reduced relative to the pressure in thesurroundings (ie the “negative pressure” in the first chamber 22 a) fromexceeding a predetermined negative pressure value of 120 mmHg.

The second tubular connector 26 further engages with a pressure sensor32 via the opening in the free end of its side tube 26 c. The pressuresensor 32 is embedded in the PCB 40 and detects the level by which thepressure in the second chamber 26 a is reduced relative to the pressurein the surroundings (ie the “negative pressure” in the second chamber 26a). The pressure sensor 32 is operably coupled to the vacuum pump 10 viathe PCB 40 such that the vacuum pump 10 is deactivated when the negativepressure in the second chamber 26 a reaches the desired negativepressure value.

The apparatus 1 further comprises an integral power source (not shown)for the vacuum pump 10 in the form of a battery pack and is containedwithin in a housing (not shown).

The tubular connectors 22,26 are formed from injection mouldedthermoplastic elastomer, which is relatively soft compared with thematerial of the components with which they engage, namely the vacuumport 12, one-way valve 24, the port 28, the pressure release valve 30and the pressure sensor 32. Accordingly, the tubular connectors 22,26deform slightly in the regions that engage with the other components,ensuring good surface contact and hence a substantially air-tightconnection between the components without the need for precisionassembly.

In use, an occlusive dressing is applied over a wound that is to betreated. The occlusive dressing is traversed by a tube that is attachedto the port 28 using a standard luer lock mechanism in order to form asubstantially air-tight connection between the apparatus 1 and thewound. The vacuum pump 10 is then activated, which extracts gas from thefirst chamber 22 a via the vacuum port 12 and the opening at the end ofits primary tube 22 b that is proximal to the vacuum pump 10, thusgenerating a negative pressure in the first chamber 22 a. The pressurerelease valve 30 permits the entry of gas into the first chamber 22 afrom the surroundings, and thus prevents the negative pressure in thefirst chamber 22 a from exceeding 120 mmHg, which is generally regardedto be the maximum negative pressure that can be safely applied to awound.

The generation of a negative pressure in the first chamber 22 a createsa pressure differential between the first chamber 22 a and the secondchamber 26 a, resulting in the passage of gas through the one-way valve24 from the second chamber 26 a into the first chamber 22 a and hencethe generation of a negative pressure in the second chamber 26 a. As thepressure release valve 30 prevents the negative pressure in the firstchamber 22 a from exceeding 120 mmHg, the negative pressure in thesecond chamber 26 a also cannot exceed 120 mmHg. The pressure sensor 32detects the negative pressure in the second chamber 26 a and deactivatesthe vacuum pump 10 when the negative pressure in the second chamber 26 areaches a predetermined value. The negative pressure in the secondchamber 26 a at which the vacuum pump 10 is deactivated may be setelectronically and may range from 80-120 mmHg.

Following deactivation of the vacuum pump 10, the negative pressure inthe first chamber 22 a may drop as a result of the entry of gas into thefirst chamber 22 a through the pressure release valve 30 or the body ofthe vacuum pump 10. The one-way valve 24 prevents the passage of gasfrom the first chamber 22 a into the second chamber 26 a, and henceprevents the negative pressure in second chamber 26 a from dropping inresponse to any drop in the negative pressure in the first chamber 22 a.

As the second chamber 26 a is in direct fluid communication with thewound via the port 28, the negative pressure in the second chamber 26 ais the same as that applied to the wound. Accordingly, the negativepressure in the second chamber 26 a may fluctuate due to movement of thepatient or direct pressure applied to the wound, and in particular maydrop as a result of the occlusive dressing not forming a complete sealaround the wound.

The pressure sensor 32 detects the negative pressure in the secondchamber 26 a and causes activation of the vacuum pump 10 when thenegative pressure in the second chamber 26 a drops below a predeterminedvalue. The negative pressure in the second chamber 26 a at which thevacuum pump 10 is activated may be set electronically and may range from80-120 mmHg and must be lower than the negative pressure at which thevacuum pump 10 is deactivated. The vacuum pump 10 continues to operateuntil the negative pressure in the second chamber 26 a reaches thepredetermined value at which the vacuum pump 10 is deactivated. Theapparatus thus maintains the negative pressure that is applied to awound at a substantially constant level for as long as is required.

1. An apparatus for negative pressure wound therapy comprising: a sourceof reduced pressure; a first chamber in fluid communication with thesource of reduced pressure such that the source of reduced pressure isoperable to generate a negative pressure in the first chamber; apressure release means that prevents the negative pressure in the firstchamber from exceeding a predetermined negative pressure value; a secondchamber comprising means for establishing fluid communication betweenthe second chamber and a wound; a valve located between the firstchamber and the second chamber, the valve permitting the negativepressure in the second chamber to increase in response to an increase inthe negative pressure in the first chamber, and preventing the negativepressure in the second chamber from dropping in response to a drop inthe negative pressure in the first chamber.
 2. The apparatus of claim 1,wherein the predetermined negative pressure value is 120 mmHg or higher.3. The apparatus of claim 1 further comprising a means for detecting thenegative pressure that is applied to the wound.
 4. The apparatus ofclaim 3, wherein the means for detecting the negative pressure that isapplied to the wound is in fluid communication with the second chamber.5. The apparatus of claim 3, wherein the means for detecting thenegative pressure that is applied to the wound is operably coupled tothe source of reduced pressure such that the source of reduced pressureis deactivated in response to the negative pressure that is applied tothe wound reaching a desired level and/or the source of reduced pressureis activated in response to the negative pressure that is applied to thewound dropping below a desired level.
 6. The apparatus of claim 5,wherein the desired level of negative pressure that is applied to thewound is between 75 and 125 mmHg, 80 and 120 mmHg, 90 and 110 mmHg, orabout 100 mmHg.
 7. The apparatus of claim 3, wherein the means fordetecting the negative pressure that is applied to the wound is anelectronic pressure sensor such as a piezoresistive electronic pressuresensor.
 8. The apparatus of claim 1, wherein the source of reducedpressure is a vacuum pump.
 9. The apparatus of claim 1, wherein thesource of reduced pressure has a maximum dimension of less than 100 mm,less than 80 mm, less than 60 mm or less than 40 mm.
 10. The apparatusof claim 1, wherein the source of reduced pressure occupies a volume ofless than 10 cm³, less than 8 cm⁴, less than 6 cm³ or less than 4 cm³.11. The apparatus of claim 1, wherein the maximum power consumption ofthe source of reduced pressure is less than 5 W, less than 3 W or lessthan 2 W.
 12. The apparatus of claim 1, wherein the first and secondchambers are defined by housings.
 13. The apparatus of claim 12, whereinthe housing of the first chamber and the housing of the second chamberare structurally the same.
 14. The apparatus of claim 12, wherein thehousings comprise a relatively soft material in at least the regions inwhich they engage the other components of the apparatus.
 15. Theapparatus of claim 14, wherein the relatively soft material is athermoplastic elastomer such as thermoplastic polyurethane orstyrene-butadiene rubber.
 16. The apparatus of claim 1, wherein thevolume of each of the first chamber and the second chamber is less than5 cm³, less than 3 cm³, or less than 1 cm³.
 17. The apparatus of claim1, wherein the valve located between the first chamber and the secondchamber is a one-way valve.
 18. The apparatus of claim 17, wherein thevalve located between the first chamber and the second chamber is adiaphragm valve.
 19. The apparatus of claim 1, wherein the pressurerelease means operates by permitting the entry of gas into the firstchamber.
 20. The apparatus of claim 19, wherein the pressure releasemeans communicates between the first chamber and a source of gas. 21.The apparatus of claim 19, wherein the pressure release means is a flowrestrictor.
 22. The apparatus of claim 21, wherein the pressure releasemeans is a precision orifice.
 23. The apparatus of claim 1, wherein themeans for establishing fluid communication between the second chamberand a wound comprises a Luer lock or another conventional medicalconnector.
 24. A system for negative pressure wound therapy comprising:an apparatus for negative pressure wound therapy according to claim 1;and, a wound dressing for negative pressure wound therapy in fluidcommunication with the second chamber of the apparatus.
 25. A kit fornegative pressure wound therapy comprising: an apparatus for negativepressure wound therapy according to claim 1; and, a plurality of wounddressings for negative pressure wound therapy adapted for theestablishment of fluid communication with the second chamber of theapparatus.
 26. A method of negative pressure wound therapy comprising:applying a wound dressing for negative pressure wound therapy to awound; establishing fluid communication between the wound dressing andthe second chamber of the apparatus according to claim 1; and,activating the apparatus.
 27. The system of claim 24, wherein the wounddressing comprises a wound contact layer of soft silicone gel.
 28. Thesystem of claim 27, wherein the layer of soft silicone gel includes gapsor perforations.
 29. The system of claim 24, wherein the wound dressingcomprises a superabsorbent material.